Wire cut electric discharge machines are generally provided with a machining fluid supply device which has a machining fluid supply source including a pressure pump, etc., so as to supply machining fluids from upper and lower nozzles, respectively connected to the supply device and arranged above and below a workpiece, to a gap between the workpiece and a wire electrode, to thereby cool the workpiece and the wire electrode and remove sludge from the gap, and further to maintain the workpiece and the wire electrode in a suitably insulated state. The amount of the machining fluid discharged from the pressure pump is controlled in a multi-stage fashion in accordance with the values of various machining parameters such as wire feed speed, thickness of the workpiece, diameter of the wire, etc. The amount of machining fluid supplied varies in accordance with the parameter values.
In wire cut electric discharge machines, electric discharge machining is performed in either of two machining modes, i.e., a cut-out operation mode for cutting a semi-finished product of a desired shape out of a workpiece or cutting a portion of a desired shape out of a workpiece or semi-finished product, and a face machining mode for, e.g., finishing the cut surfaces of a workpiece or semi-finished product after a cut-out operation. To control the amount of the machining fluid supplied from the upper and lower nozzles to values suited to the different machining modes, a conventional machining fluid supply device comprises first and second flow regulating valves which are disposed in first and second pipes respectively connecting the upper and lower nozzles to the pressure pump, and the openings of these two flow regulating valves are manually adjusted to different values, depending on whether the cut-out operation or face machining is to be carried out. It is, however, very troublesome to carry out a manual adjustment every time the machining mode is switched from cut-out operation to face machining or vice versa. Further, where both a cut-out operation and face machining are involved, unmanned operation of the electric discharge machine is not available because the flow rates of the machining fluids must be manually adjusted.